Production of unsaturated nitriles



' in the molecule.

Patented Sept 25, 1945 'UNlTED STATES PATENT OFFICE PRODUCTION OF UNSATURATED NITBILES Le Roy U. Spence, Elkins Park, Pa., assignor to Rlihm a Bass Company, Philadelphia, corporation of Delaware Application January 27, 1942,- Serial No. 428,377

' N Drawing.

4 Claims.

This inventionrelates to the production of unsaturated aliphatic nitriles. It involves the formation of such unsaturated nitriles by the dehy-. ,drohalogenation of saturated, chlorinated or bro- .less difllculty than by the methods known heretofore. Earlier methods involve at least one of two major difficulties, namely the use of high temper- 'atures or the consumption of additional reagents. Both of these procedures are costly. Heretofore it has been customary'to heat the halogenated nitriles together with inorganic bases or with amines which reacted with the liberated hydrogen halide whereby unsaturation of the nitrile resulted. The disadvantage of these prior processes is that reagents are continually being consumed, thus add- 2 ing to the cost of operation.

This invention is particularly unique in that it involves a catalytic reaction which can be operated at lower temperatures without the necessity of employing materials which react and combine with the nitriles or with the decomposition prod-' ucts thereof. Furthermore, the yields of the desired products are high. Essentially, this inven- Pa., a

tion consists of heating a halogenated nitrile in the presence of an amine hydrohalide which acts catalytically at temperatures of about 150 C. to

about 250 C. The catalyst is preferably used as a molten salt in a still fitted with a'fractionating column and condenser. While the temperature may be regulated over wide ranges by the ratio of nitrile and amine salt, it is desirable to maintain the temperature between 150-250 C. and the preferred range is ISO-180 C. The chlorinated or brominated nitrile may be added gradually to the heated molten salt catalyst which is maintained at a temperature within the range aforesaid. The unsaturated nitrile, hydrogen halide, and any unchanged chlorinitrile or bromonitrlle pass into the iractionating column, which returns the unchanged nitrile and allows the'unsaturated nitrile and hydrogen halide to be removed from the top of the column. Alternatively, the fractionating column may be eliminated and the mixture of the unsaturated nitrile, hydrogen halide, and unchanged saturated nitrile may be washed with and cycloaliphatic amine hydrochlorides and hydrobromides are suitable catalysts, provided that these are stable at the temperature of the dehydrohalogenation reaction. Among the catalysts suitable for use in my process may be included the hydrochlorides and hydrobromides of cetyl dimethyl amine, lauryl dimethyl amine, di-Z- ethyl hexyl amine, dimethylamine, lauryl methyl amine, dibutylamine, diamylamine, trlamylamine, dlcyclohexyl amine, benzyl dioctylamine.

The saturated halogenated nitriles which may be dehydrohalogenatedto the corresponding unsaturated nitriles are those containing from 3 to 8 carbon atoms. Included in this group are 1,153- trichloropropionitrile, a,-fl-dichl0ropr0pionltri1e, a.- chloroisobutyronitrile, a-ethyl-a-chloropropionitrile, a-propyl-a-ch10r0proplonitrile, ,a-dichl0ropropionitrile, a-bromoisobutyronitrile, afl-diblomopropionitrile, etc. The reaction, like catalytic reactions in general, is specific and is limited to compounds or certain definite configuration. For example, a-chloropropionitrile cannot be satisfactorily dehydrohalogenated by this process, and it is only when the molecule contains additional alkyl or halogen groups that the dehydrohalogenation will take place. The compounds, which may be successfully dehydrohalogenated by this process, are identified by the general formula:

CHzX-CZY-CN where X is chlorine or bromine or hydrogen, Y is chlorine, bromine, hydrogen or an aliphatic group containing 1 to 5 carbon atoms, and Z is either chlorine or bromine and in which formula the total number. of substituting groups, other than hydrogen, is at least two. By the dehydrohalogenation of compounds of this general formula there are obtained products which have a conjugated system, C=C-CEN, and, as such, these compounds exhibit unusual characteristics, notably the tendency to polymerize.

Furthermore, these unsaturated nitriles may be converted to corresponding unsaturated amides, esters, and acids which are also valuable in the preparation oi polymeric materials.

The following examples will serve to illustrate this invention.

Example 1 that part of the liquid could be taken oil and the rest returned as reflux to the column. The top 01' the reflux condenser was connected to a water scrubber which was used to collect I-ICl formed in the reaction.

The amine hydrochloride was heated to about 170 C. and u,,p-trichloropropionitrile (CHaClCClaCN) was gradually added to the flask, while the temperature was maintained at 165-170 C. The trichloropropionitrile used had a boiling point of 156-157(!. and N 1.4677, and contained a small amount of ,p3-dichloropropionitrile as an impurity. Afterabout 40 cc. of trichloropropionitrile was added to the flask, refluxing in the column began and the temperature at the top of the column increased to about 130 C. and considerable HCl evolved. The addition of the trichloroproplonitrile was continued while the flask temperature was held at 165-170 C. The takeofl' from the top of the column was so regulated as to keep the temperature at 130-135 C. After 192 g. (1.212 mols) of trichloropropionitrile had been added, the temperature in the flask was increased to about 185 C. and distillation was completed. The distillate weighed 142 g. and the yield of HCl, as determined by titration of the water scrubber, was 0.805 mol or 66% of theory.

The distillate was redistilled through a i'ractionating column in orderto separate the various compounds present, and the iollowing fractions were obtained:

Fraction B. P. Np Weight Fraction A consisted chiefly of a-chloroacrylonitrile (B. P. 88 0., N 1.4294) produced presumably from afi-dichloropropionitrile originally present as an impurity. Fraction B consisted of .chloroacrylonitrile and the yield of the latter based on the amount or decomposed trichloropropionitrile was 69% of theory.

Example 2 One mol of a,,p-trichloropropionitrile was refluxed in the absence of catalyst for a period of three hours. During this time there was no evidence of decomposition and at the end of, the period the material distilled normally at its original boiling point.

Example 3 The process of Example 1 was repeated with 21 g. of d1-2-ethyl hexylamine hydrochloride serving as catalyst. A total or 836 g. of p-trichloropropionitrile was heated in the presence or the catalyst, and 62% of this was converted to dichloroacrylonitrile. The final yield was 81% of theory, based on the amount of trichloropropionitrile which had been decomposed.

Example 4 when 319 g. of ,a,,8-trichloropropionitrile-was heated in the presence of g. of lauryl dimethylamine hydrochloride as a catalyst, 62% oi.

the former was decomposed and an 82.5% yield,

calculated as above, of dichloroacrylonitrile was obtained. 7

Example 5 When 181 g. of ,,p-trichloropropionitrile was heated in the presence or g. of dimethylamine hydrochloride as a catalyst, 32% 01' the former was decomposed, and a 39% yield, calculated as above, oi. dichloroacrylonitrile was obtained.

Example 6 Hours 01 Per cent conver- Grams of Per cent d of OHICICCIQCN gg; gggf ono1= OlON 298 2. 0 45. 7 76. 5 $5 2. 0 55. 6 B9. 2 E5 2. 0 57- 8 W. 1 m6 1. 7 61. 2 87. 3 370 2. 5 48. 0 88. 5

The yield in the flrst run was low because of the trapping or retention of the trichloropropionitrile in the equipment. It will be noted that the catalyst remained active on continued use.

Example 7 One mol of a,p-dichloropropionitrile (N 1.4655) was heated in the presence of 20 g. or di-2-ethyl hexyl amine hydrochloride as catalyst according to the method 0! the previous examples. An yieldoi' a-chloroacrylonitrile (B. P. 87-89 0., N 1.4297) was obtained.

Example 8 A sample of a-chloroisobutyronitrile (B. P. 118 (3., N 1.4051) was converted to methacrylonitrile (B. P. 92 (2., N 1.4002) by the method described above, by the use of di-2-ethylhexyl amine hydrochloride as a catalyst. The

yield of methacrylonitrlle, based on the amount of decomposed reactant, was 83% Example 9 One mol 0! ap-dicromoproprionitrile was converted to a-bromoacrylonitrile by the method described above by the use of di-2-ethyl-hexyl 5 amine hydrobromide as a catalyst. The yield of abromoacrylonitrile, based on the amount of decomposed reactant, was over 70% I claim:

1. A process for the production of unsaturated nitrlles which comprises heating at temperatures of about 150 C. to about 250 C., in the presence of a catalytic amount of an aliphatic amine hydrohalide, saturated, halogenated aliphatic nitriles from the group consisting of a-ha1oisobutyronitrile, ,p-diha1oisobutyronitrile, a,fi-d1- halopropionitrfle, and a,,p-trihaloproprionitrile. 

